﻿#define _CRT_SECURE_NO_WARNINGS   1

#include<math.h>

#include<stdio.h>

#define PI acos(-1)

int main()

{

	double h = 0;

	double r = 0;

	scanf("%le %le", &r, &h);

	double c = 2 * PI * r * h;

	printf("%2lf", c);

	​return 0;

}